Respective electrical actuators are known for example from the oil and gas industry for the operation of valves. Such valves include gate valves, chokes, ball valves, blow-out-preventers (BOP) or the like. In an application using the respective valves, an emergency measure is required in case of an energy failure, to adjust the valves to their closed or open position or alternatively secure the valves in their current position against the pressure of, for example, produced mineral oil. In this context, the two modes are referred to as “fail save close/open” and “fail as is”. In the “fail save close/open”-mode, the valves are automatically adjusted to the closed/opened position by the assigned electrical actuator in the event of an energy failure and missing actuation. This may be achieved for example by pre-stressed spring packages or the like. In the “fail as is”-mode, the valves stay in the position that have assumed during the energy failure. Therefore, often a “fail as is” device is necessary, which holds the valve in the opened position, partly opened position, or in the position at the moment of the energy failure. At the same time, holding the valve in its current position should be achieved without the use of energy.
In some embodiments, electrical actuators such as those described in WO 2011/009471 A1 or WO 2011/006519 A1 are employed. The electrical actuator is, for example, coupled to the valve from outside and includes one or more electric motors. The motors drive a drive shaft, which may drive a respective gear shaft by means of a transmission gear. In some cases, the gear shaft may be used for directly turning a respective valve member via an adapter or the like. It is also possible that the rotational movement of the gear shaft is convertible into a linear movement by a ball-type linear drive or the like. The linear movement then serves for the linear adjustment of the respective valve member.
An object of the present disclosure is to improve a respective electrical actuator such that it is provided with a “fail as is”-device without requiring the use of a stronger motor, while having a simple, reliable and cost-effective construction.
This object is achieved by the features of claim 1.
In accordance with various embodiments a return stop device is included as an additional member within the electrical actuator that functions in both rotational directions of the drive or gear shaft. The return stop device comprises a pot-shaped outer part and a hub part, which is rotatably supported therein. The hub part is connected to the gear shaft in a torque-proof manner. Additionally, a free space is formed between the hub part and the outer part, and a wedging member is situated in the free space. Rotation of the drive shaft causes the wedging member to transition to a free rolling position, enabling the hub part to rotate relative to the outer part.
If, however, a respective torque acts upon the drive shaft from the side of the attached valve, e.g. via the gear shaft and the hub part, then no movement of the wedging member takes place to transition the wedging member to the free-rolling position. Instead, the wedging member stays in the wedging position and a turning back of the drive shaft caused by the attached valve is prevented.
Thus, in accordance with various embodiments, the return stop device is designed such that the wedging member prevents valve-induced rotation of the drive shaft and the gear shaft.
This means that the return stop device enables an unrestricted actuation by the drive shaft and the gear shaft for adjusting for the valve member in both rotational directions of the drive shaft. If, however, retroactive torques act on the drive shaft via the gear shaft from both sides of a wall member, then the return stop device blocks movement in both rotational directions.
The return stop device is arranged between the drive shaft and the gear shaft and comprises minimal parts, resulting in a simple, reliable and cost-efficient construction is the result. Besides that, the structure of the return stop device is very robust and compact, such that the installation space is small. According to the construction of the return stop device, moreover, during holding of the respective position in the “fail as is”-mode, no energy is required. Additionally, a stronger electric motor is not required for the electrical actuator because the return stop device enables an unimpeded driving in both directions when operating the drive shaft.
A simple installability and assignability of the respective parts of the return stop device is given for example when the outer part has a cylindrical inner side facing the hub part and the hub part has at least two wedging surfaces facing this inner side. Between the inner side of the outer part and each wedging surface, a roller-shaped wedge element is arranged as a wedging member. The wedging member—in particular, one of the wedge elements—is moved into the free rolling position by an adjusting element of the drive shaft. Thus, depending on the rotational direction of the drive shaft, one of the roller-shaped wedge elements may be moved into the free rolling position, while the other roller-shaped wedge element is practically arranged in an idle state or free wheel, respectively.
In some embodiments, the adjusting element comprises an adjusting pin arranged essentially in parallel to the drive shaft. The adjusting pin may be offset by a distance from the drive shaft.
Various electric motors are applicable for such an actuator. In some embodiments, two electric motors may be used to provide additional redundancy. In a simple embodiment, the drive shaft may be formed by a rotor of the electric motor. The respective stator may be fixed in the housing of the actuator.
A coupling between the gear shaft and the drive shaft enables rotation of the drive shaft to induce a corresponding rotation to the gear shaft. In some embodiments, the hub part has at least two coupling elements and the drive shaft has at least two counter-coupling elements, where the coupling elements engage or are engaged by the counter-coupling elements. This provides a rotational connection between the hub part (and thereby the gear shaft), and the drive shaft, where the hub part and the drive shaft are at least partly in mesh with each other. In some embodiments, a designed tolerance of the coupling elements and counter-coupling elements allows some rotational movement of either the hub part or the drive shaft before the coupling and counter-coupling elements engage each other. Additionally, the coupling pin may comprise a driving pin and the counter-coupling element may comprise a pin hole.
Since the respective coupling also is at hand, if the return stop device becomes operative, then it may prove advantageous if the coupling element and the counter-coupling element are in engagement with other under a clearance.
In some embodiments, the wedge elements may be biased away from each other by a compression spring between the elements. This allows the wedge elements to be biased to their wedge positions in the absence of influence by the adjusting element of the drive shaft.
The adjusting element may engage the wedge element by protruding from the drive shaft into the free space and being arranged in a circumferential direction of the hub part on both sides of the wedge elements. Depending on the rotational direction of the drive shaft, one of the adjusting elements will then move the respective wedge element into the free rolling position, thus enabling an according rotation of the drive shaft (and hub part) and the gear shaft.
The outer part of the return stop device is arranged unrotatably, which is achieved for example by fixing the outer part to the housing of the actuator.
The wedge surfaces are arranged at the hub part and may be designed in a variety of ways. In one embodiment, the wedge surfaces may essentially taper slantingly towards the inner surface of the outer part, such that the free space between the hub part and the inner surface of the outer part tapers to a clearance that is at least smaller than the wedge elements. Thereby, the two wedge surfaces are facing away from each other and each of the wedge surfaces is assigned to a respective wedge element.
In order to provide sufficient space for adjusting the wedge element and for positioning the compression spring, a center surface extending perpendicularly to a diameter of the outer part may be arranged between the wedge surfaces. Along this center surface, for example the compression spring is arranged, while on both sides of the center surface, the respective wedge surfaces are arranged with wedge elements arranged thereon.
A torque-proof connection between the hub part and the gear shaft exists, for example through the hub part being connected to the drive shaft by positive fit and especially by means of a key.